> >asks for US-friendly replacements for `boffin' and `motor-mower engine'.
> >and a motor-mower engine is the sort of lawnmower run by petrol (gas)
>

It sounds like "motor-mower" should definately be "lawnmower".
If you mean one that is not pushed but actually "sat" upon,
then it is variously called a "riding mower", a "lawn tractor"
or a "garden tractor" (with increasing prices according to my
1984 Sears catalog).

I can't help you with "boffin" (before my time) but I'll run it
by my father and see what he thinks.